1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for estimating time-shifts per event and per trace in the extraction of multi-dimension linear events.
2. Discussion of the Background
Seismic data acquisition and processing may be used to generate a profile (image) of the geophysical structure under the ground (subsurface). While this profile does not provide an accurate location for oil and gas reservoirs, it suggests, to those trained in the field, the presence or absence of such reservoirs. Thus, providing a high-resolution image of the subsurface is desired, for example, by those who need to determine where oil and gas reservoirs are located.
Reflection seismology is a method of geophysical exploration to image the subsurface of the earth for determining its properties, which information is especially helpful in the oil and gas industry. Typically, a controlled source sends seismic energy waves into the earth. By measuring the time (travel-time) it takes for the reflections to come back to plural receivers, it is possible to estimate the depth and/or composition of the features causing such reflections. These features may be associated with subterranean hydrocarbon deposits.
However, there are certain problems associated with processing the reflections measured by the receivers as discussed now with regard to FIG. 1. FIG. 1 shows a seismic system 10 that includes at least a source S1 and plural receivers R1 to R3. The source S1 emits energy, as waves 12, 14, and 16, that propagates through a surface layer 20 and other layers 22 until is reflected by a structure 24. Part of the energy may also propagate through the structure 24 into further layers 26 until reflected by another structure (not shown). The reflected waves return to the earth surface 30, where the receivers R1 to R3 record them.
However, the near-surface layer 20, i.e., the top-most layer of the earth, often causes significant difficulties for imaging seismic reflection data because this layer, through its irregular thickness and/or velocity structure, causes timing and phase differences between reflection events recorded at neighboring receivers, for example, at receivers distributed along a cross-line direction OY (e.g., R1 and R1′). In addition, the near-surface layer promotes source-generated coherent noises which often mask the reflections.
To correct these problems, it is customary in the field to apply time-shifts to the seismic traces to account for transit time for the near-surface layer, which is known in the field as the “static shift approximation.” This approximation works well when the seismic travel paths through the near-surface layer, as illustrated in FIG. 1, are near-vertical. Thus, all the travel paths through the near-surface layer are substantially identical and the travel-times are substantially identical.
However, that is not the case for all actual situations. For example, if the near-surface layer has a higher velocity than the underlying layers, and/or the near-surface travel path segments 200 are not vertical and coincident as illustrated in FIG. 2, the traditional static shift approximation does not work. In addition, there may be more than one travel path along which significant seismic energy may travel from the source to the receiver, leading to “multi-path” arrivals. Because the patterns of these arrivals can change from trace to trace, it is clear that applying relative time-shifts, as traditionally performed, cannot address the underlying phenomena.
Thus, there is a need to provide a computing device and a method that estimate and compensate for all the significant arrival delays embedded in each seismic trace.